1. Field of the Invention
This invention relates to a method of manufacturing an electronic part and, more particularly, to a method of manufacturing an electronic part provided with resin layers formed on a periphery of the electronic part, the resin layers being formed by dipping the electronic part into resin.
2. Description of the Prior Art
In a method of cleaning an electronic part, an enviromentally safe use of cleaning method such as a cleaning method using water is planned for abolishing use of an ozone layer damaging material and an environmentally pollutive material such as a freon, trichloroethane and the like. As one conventional example of an electronic part capable of being cleaned with water, an electronic part having a multilayer structure of a resin outer coat is shown in FIG. 5(a) and FIG. 5(b).
As shown in FIG. 5(a) and FIG. 5(b), a piezoelectric resonator 1 is one example of the electronic part. The piezoelectric resonator is comprised of a strip-shaped resonator element 2 constituting an electronic part body, a pair of terminals 3, 3 which hold the element by pinching it at both ends and are connected to electrodes of the element, a first resin layer 4 and a second resin layer 5. A cavity 6 is formed to prevent impairing vibration of a vibrating portion having vibration electrodes. As shown in FIG. 4, the resonator element 2 is provided with vibration electrodes 8, 8 disposed opposite to each other on two opposing surfaces of a piezoelectric substrate 7.
Manufacture of the above piezoelectric resonator 1 is performed as described below. After holding the resonator element 2 by pinching it at both ends with the pair of terminals 3, 3, the terminals are connected and bonded to the electrodes. The first resin layer 4 is formed by coating the surfaces of the electrodes 8, 8 on the piezoelectric substrate 7 with wax 9, thereafter as shown in FIG. 6(a), the surfaces of the piezoelectric resonator element 2 are coated with resin by dipping them into a resin bathtub, leaving the end portions of the terminals 3 uncoated. Furthermore, as shown in FIG. 6(b), the second resin layer 5 is formed on the surface of the first resin layer 4 by dipping the coated element into a second resin bathtub, thus the outer coat is formed in multilayers and set by heat. In addition, when necessary, as shown in FIG. 6(c), a final resin layer 10 is formed on the surface of the second resin layer 5 by dipping the coated element into a final resin bathtub and is set by heat, thereby to produce a dense layer on the surface and increase strength of the layer. By heat-setting the resin of the first resin layer 4, the wax is melted and diffused into the resin, so that a cavity is formed for vibration in the vibrating portion.
However, in the above conventional manufacturing method of an electronic part, there is a problem that when dipping the element into the resin, an area of the element covered by the resin becomes less in an upper portion of the element. That is, the amount of resin is less near the roots of the terminals 3 of the electronic part. Thus, gaps are generated near the roots of the terminals, thereby allowing water to invade. Particularly, when the number of times an element is dipped increases, the resin surrounding the upper portion of the element becomes worse as the number of dipping times increases.